Broadband reciprocal dual meander line ferrite phase shifter



June 3, 1969 J. K. PARKS BROADBAND RECIPROCAL DUAL MEANDER LINE FERRITE PHASE SHIFTER Filed May 25, 1967 Sheet 2, of 2 MAGNETIC FIELD PATTERN FIELD PATTERN 26 MAGNETIC FIG.2.

INVENTOR. J05 K. PARKS ATTORNEY United States Patent 3,448,410 BROADBAND RECIPROCAL DUAL MEANDER LINE FERRITE PHASE SHIFTER Joe K. Parks, Clearwater, Fla., assignor to Sperry Rand Corporation, a corporation of Delaware Filed May 25, 1967, Ser. No. 641,343 Int. Cl. H03h 7/30 US. Cl. 3333I 4 Claims ABSTRACT OF THE DISCLOSURE A phase shifter having a reciprocal phase delay characteristic substantially independent of frequency comprising a pair of folded strip line (meander line) conductors parallel to each other with each line being mirror symmetric with respect to the facing side of the other line. A ferrite slab is located midway between the two meander lines. An input microwave signal is applied to one end of each of the lines with the same amplitude and the same phase. The other ends of the two lines are combined to provide a phase delayed output signal.

Background of the invention The development of microwave devices continually is direction toward designs which provide minimum bulk and weight. Such designs are mandatory in the case of the complex electronic systems required in modern airborne applications. Among the various components required in airborne phased array radars, for example, broadband reciprocal phase shifters have presented a particularly diflicult problem because of the large numbers which are involved. Compact ferrite phase shifter devices have been proposed utilizing strip line fabrication techniques but these either produce nonreciprocal amounts of phase shift or provide reciprocal phase shifts over only a very narrow frequency band.

Summary of the invention Substantially purely reciprocal phase shift is achieved in a lightweight and compact device in accordance with the present invention by the provision of dual parallel meander lines which are excited with equal amplitude and equal phase microwave energy. Each meander line is mirror symmetrically identical to the facing surface of the other line. The resultant R.F. magnetic field midway between the two meander lines is substantially only linearly polarized in a direction perpendicular to the planes of the lines. This magnetic field orientation is preserved irrespective of the frequency of the microwave signal. A ferrite slab, placed in the region of the resultant linearly polarized RF. magnetic field, introduces the same phase delay in the RF. energy propagating along the meander lines independent of the direction of propagation.

Brief description of the drawings FIGURE 1 is a perspective view of a partially disassembled embodiment of the invention; and

FIGURE 2 is a sketch of the RF. magnetic field configuration within the embodiment of FIGURE 1.

Description of the preferred embodiment Referring to FIGURE 1, a ferrite slab 1 is positioned between a pair of meander lines formed on insulating boards 2 and 3. The meander line on board 2 (hidden from view) is mirror symmetrically identical to meander line 4 and board 3 so that the facing surfaces of the meander lines precisely match each other in every respect. It is convenient to form the meander lines by etching copper clad insulating boards in a conventional manner.

Insulating boards 2 and 3 are mounted on conductive slabs 5 and 6, respectively. Two strips of dielectric material 7 and 8 are mounted on board 2 on respective sides of ferrite slab 1. Strips 7 and 8 have the same thickness and length as slab 1. Input microwave energy is supplied via coaxial line coupler 9 and matching transformer and power divider 10 to the input terminals (such as terminal 11 of line 4) of the meander lines with the same amplitude and phase. An identical matching transformer and power divider 13 is coupled to the output terminals (such as terminal 12) of the meander lines for combining the delayed signals and applying the same to output coaxial line coupler 14. The phase shifter of FIGURE 1 is structurally and operationally symmetric with respect to its input and output ports. The phase shifter is assembled by mounting slab 6 across coaxial line couplers 9 and 14 with meander line 4 facing ferrite slab 1 and screws 15 engaging slots 16 in coupler 9 and screws 17 engaging slots 18 in coupler 14.

Reciprocal phase shift is achieved in the embodiment of FIGURE 1 by producing a resultant R.F. magnetic field, in response to the flow of microwave energy along the dual meander lines, which is substantially linearly polarized in a direction perpendicular to the planes of the meander lines at a location substantially midway therebetween. The production of the aforesaid magnetic field orientation can be understood by reference to FIG- URE 2 which is similar to a longitudinal sectional view of FIGURE 1. The ferrite slab has been omitted from FIGURE 2 in order to avoid confusion with the draftsmans construction lines depicting the magnetic field configuration. As previously mentioned, the meander lines are fed by microwave energy of the same amplitude and same phase so that the amplitudes and phases are the same at corresponding points of the lines such as points 19, 20 and 21, 22 and 23, 24 and so on. Assuming that the direction of microwave current through points 19 and 20 of the respective meander lines momentarily are toward the observer in the View of FIGURE 2, circular magnetic field patterns 25 and 26 intersect at a point of interest 27 along a plane parallel to and equally distant between the meander lines. Tangents 28 and 29 (drawn to the respective field patterns 25, 26) are of equal amplitude and time phase and are equally angularly displaced with respect to line 30 which is perpendicular to the meander lines and passes through point 27. It can be seen that although it varies in amplitude and sense, the vector resultant of magnetic fields 28 and 29 always lies along line 30 irrespective of the time phase of the microwave energy flowing through points 19 and 20 of the meander lines.

A similar graphical construction has been made about a second arbitrarily selected point of interest, point 31, along the plane which is equally distant between the meander lines. Vector 32 represents the amplitude and direction of the magnetic field attributable to the current flowing through point 19 whereas vector 33 represents the magnetic field at point 31 attributable to the current flowing through point 20. It will be noted that the angular displacement between the magnetic field component vectors is reduced as the distance increases between the point of interest and points 19 and 20. However, the resultant magnetic field vector still lies along a line (34) which is perpendicular to the meander lines. Thus, the resulting magnetic field at any point along a plane which is equally distant from the meander lines is substantially linearly polarized in a direction perpendicular to the, meander lines irrespective of the frequency of the microwave signal flowing through the meander lines. This follows from the fact that the magnetic field contributions at points 27 and 31 and at all other points along the same plane attributable to currents flowing through points 21 and 22 and through points 23 and 24 and all other corresponding pairs of points likewise produce a resultant linearly polarized magnetic field as shown in the constructions relating to the currents flowing through points 19 and 20. The resultant linearly polarized magnetic field provided by the dual meander line configuration of the present invention requires only that said lines be mirror symmetrically identical and be fed with microwave energy of the same amplitude and phase.

Ferrite slab 1 is placed in the position of the plane containing points 27 and 31 and introduces the same phase delay in the microwave signal propagating along the meander lines for either direction of propagation whereby the phase delay characteristic is reciprocal. Reciprocity is maintained irrespective of the frequency of the microwave signal. The magnitude of the phase delay is a function of the magnitude of the total magnetic field; accordingly, the phase delay may be controlled by means of a variable D.C. magnetic field which may be provided for biasing ferrite slab 1 in a conventional manner.

While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description rather than limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of the invention in its broader aspects.

I claim:

1. A broadband reciprocal phase shifter comprising:

a ferromagnetic material containing a given plane,

said material being adapted to be biased by a DC.

magnetic field, and

means for producing an alternating magnetic field substantially linearly polarized irrespective to the frequency of said field, the direction of polarization of said field being perpendicular to said plane, said means comprising:

a pair of folded strip meander lines parallel to said plane and equally distant therefrom,

each of said lines being mirror symmetrically identical to the facing side of the other line,

means for applying an input alternating signal to one end of each of said lines with the same amplitude and phase, and

means for combining the other ends of said lines to provide an output port for said input signal.

2. Apparatus as defined in claim 1 wherein said ferrimagnetic material is a ferrite slab.

3. Apparatus as defined in claim 1 and further including a pair of insulating boards on which said lines are respectively mounted, each said board being on the side of its respective line opposite the side facing said given plane.

4. Apparatus as defined in claim 3 and further including a pair of conductive slabs on which said boards are respectively mounted, each said slab being on the side of its respective board opposite the side facing said given plane.

References Cited UNITED STATES PATENTS 3,164,790 1/1965 Oh 333-10 3,289,115 11/1966 Carr 333-24.1 X

HERMAN KARL SAALBACH, Primary Examiner.

P. L. GENSLER, Assistant Examiner.

US. Cl. X.R. 

